R

Figure 3.19 The appearance of a 2-deuterio-fatty acid in the configuration in which it must be held on the enzyme during the elimination of the carboxyl group to give a 1-alkene. Had it been a syn elimination then the deuterium would have been cis to the alkyl group as in the third formula

3.2.1 Hydrocarbon Pheromones

A number of hydrocarbon pheromones are known, chiefly in the Diptera, but also among Lepidoptera (see later). Sometimes hydrocarbons are part of the defensive secretion, as in the confused flour beetle, Tribolium confu-sum, which uses terminal alkenes e.g., 1-pentadecene, 1-hexadecene and 1-heptadecene, formed as described above. They are frequently found accompanying terpenes or oxygenated compounds in the secretions of many social insects, and C9 to C15 alkanes frequently accompany formic acid in defensive secretions, where they are thought to act as spreading agents.

The major sex pheromone of the female housefly Musca domestica is (Z)-9-tricosene. Incubating a mixture of (Z)-15-[1-14C]- and (Z)-15-

[15,16-3H2]tetracosenoic acid with microsomes from houseflies gave equal amounts of tritiated (Z)-9-tricosene and 14C-labelled C02. Moreover, by adding hydroxylamine as a trapping reagent for aldehydes, it was possible to capture the intermediate aldehyde as its oxime (Figure 3.20). Both the cuticular hydrocarbons and the tricosene pheromone are synthesized in the integument but the integument is closely associated with oenocyte cells. The tricosene is converted by a cytochrome to the other two components of the pheromone, the epoxide (major) and the unsaturated ketone (minor) (Figure 3.20).

Figure 3.20 Demonstrating the formation of the sex pheromone of the common housefly (Z)-9-tricosene from a C24 fatty acid through the aldehyde. T indicates tritium. Note that using a mixture of tritiated and !4C-labelled compounds for this purpose is the same as having all the labels in the same molecules. The epoxytricosene is another major component of the pheromone and the tricosenone is a minor component

(Z)-14-tricosen-10-one

Figure 3.20 Demonstrating the formation of the sex pheromone of the common housefly (Z)-9-tricosene from a C24 fatty acid through the aldehyde. T indicates tritium. Note that using a mixture of tritiated and !4C-labelled compounds for this purpose is the same as having all the labels in the same molecules. The epoxytricosene is another major component of the pheromone and the tricosenone is a minor component